1. Field of the Invention
This invention relates to methods and apparatus for the medical treatment of disease of the heart. More particularly, this invention relates to a method and apparatus for treating cardiac arrhythmias by ablating in a vicinity of pulmonary venous tissue.
2. Description of the Related Art
Tissue ablation from the inner walls of hollow viscera of the body generally, and the vascular system in particular, has been found to be useful in the treatment of various medical conditions. Technological developments in intravascular catheters, manipulative instruments adapted to intravascular catheters, and catheter localization techniques have especially benefited the field of cardiology. Percutaneous transcatheter ablation has been used successfully in the treatment of conduction defects and arrhythmias of various types. Today, atrial tachyarrhythmias are a common application for ablative therapy.
Various ablative modalities have been employed in the past, such as ablation by direct heating. Energy can be conducted to the target tissue using various modalities, such as ultrasound, laser, resistive heating, and radiofrequency energy.
One ablative approach is the so-called xe2x80x9cmazexe2x80x9d technique. In general, the maze procedure attempts to block abnormal conduction patterns in the left atrium by establishing a maze-like pattern of linear lesions in the left atrial wall.
Atrial arrhythmias are known to be associated with abnormal electrical activity of tissue foci in the vicinity of the pulmonary veins, especially the superior pulmonary veins. Various ablative treatments of such foci have been attempted. For example, the production of linear atrial lesions by radiofrequency ablation, in combination with ablation of suspected arrhythmogenic foci has been performed using transcatheter techniques.
More recently, circumferential lesions at or near the ostia of the pulmonary veins have been created to treat atrial arrhythmias. U.S. Pat. Nos. 6,012,457 and 6,024,740, both to Lesh, disclose a radially expandable ablation device, which includes a radiofrequency electrode. Using this device, it is proposed to deliver radiofrequency energy to the pulmonary veins in order to establish a circumferential conduction block, thereby electrically isolating the pulmonary veins from the left atrium.
Radiofrequency ablation using multiple contiguous circumferential points, guided by electro-anatomical mapping is proposed in the document, Circumferential Radiofrequency Ablation of Pulmonary Vein Ostia: A New Anatomic Approach for Curing Atrial Fibrillation, Pappone C, Rosanio S, Oreto G, Tocchi M, Gugliotta F, Vicedomini G, Salvati A, Dicandia C, Mazzone P, Santinelli V, Gulletta S, Chierchia S, Circulation 102:2619-2628 (2000). It is emphasized that particular care must be exercised to ensure that the ablation sites are indeed contiguous; otherwise irregular electrical activity in the pulmonary vein may continue to contribute to atrial arrhythmia.
It has also been proposed to produce circumferential ablative lesions using ultrasound delivered through a balloon. This technique is described, for example, in the document, First Human Experience With Pulmonary Vein Isolation Using a Through-the-Balloon Circumferential Ultrasound Ablation System for Recurrent Atrial Fibrillation, Natale A, Pisano E, Shewchik J, Bash D, Fanelli R, MD; Potenza D; Santarelli P; Schweikert R; White R; Saliba W; Kanagaratnam L; Tchou P; Lesh M, Circulation 102:1879-1882 (2000).
A known drawback in the use of radiofrequency energy for cardiac tissue ablation is the difficulty in controlling the local heating of tissue. There are tradeoffs between the clinical desire to create a sufficiently large lesion to effectively ablate an abnormal tissue focus, or block an aberrant conduction pattern, and the undesirable effects of excessive local heating. If the radiofrequency device creates too small a lesion, then the medical procedure could be less effective, or could require too much time. On the other hand, if tissues are heated excessively then there could be local charring effects due to overheating. Such overheated areas can develop high impedance, and may form a functional barrier to the passage of heat. The use of slower heating provides better control of the ablation, but unduly prolongs the procedure.
In consideration of these, and other factors, it is appropriate, in designing a practical radiofrequency electrode, to consider the amplitude of the radiofrequency signal, the amount of time required for the energy application, the size of the electrode, and the contact area, as well as ease of positioning, withdrawal, and repositioning of the device so as to be able to conveniently produce multiple lesions during the same medical procedure.
Previous approaches to controlling local heating include the inclusion of thermocouples within the electrode and feedback control, modulation of the radiofrequency signal, local cooling of the catheter tip, and fluid assisted techniques, for example perfusion of the target tissue during the energy application, using chilled fluids. Typical of the last approach is Mulier, et al. U.S. Pat. No. 5,807,395.
Known solutions to electrical pulmonary vein isolation typically require four to seven radiofrequency applications for completion of the isolation of each pulmonary vein. Other techniques utilize a coil within an expandable balloon. Radiofrequency or ultrasound energy from the coil is passed through the balloon together with a conductive fluid, into surrounding tissue.
Publications which describe various medical techniques of interest include:
1. Scheinman M M, Morady F. Nonpharmacological Approaches to Atrial Fibrillation. Circulation 2001; 103:2120-2125.
2. Wang P J, Homoud M K, Link M S, Estes III N A. Alternate energy sources for catheter ablation. Curr Cardiol Rep 1999 July; 1(2):165-171.
3. Fried N M, Lardo A C, Berger R D, Calkins H, Halperin H R. Linear lesions in myocardium created by Nd:YAG laser using diffusing optical fibers: in vitro and in vivo results. Lasers Surg Med 2000; 27(4):295-304.
4. Eigler N L, Khorsandi M J, Forrester J S, Fishbein M C, Litvack F. Implantation and recovery of temporary metallic stents in canine coronary arteries. J Am Coll Cardiol 1993; 22(4):1207-1213.
5. Synthetic Biodegradable Polymers as Medical Devices; by John C. Middleton and Arthur J. Tipton. 1998.
6. Keane D, Ruskin J, Linear atrial ablation with a diode laser and fiber optic catheter. Circulation 1999; 100:e59-e60.
7. Ware D, et al., Slow intramural heating with diffused laser light: A unique method for deep myocardial coagulation. Circulation; Mar. 30, 1999; pp. 1630-1636.
Other medical technologies of interest are described in U.S. Pat. No. 5,891,134 to Goble et al., U.S. Pat. No. 5,433,708 to Nichols et al., U.S. Pat. No. 4,979,948 to Geddes et al., U.S. Pat. No. 6,004,269 to Crowley et al., U.S. Pat. No. 5,366,490 to Edwards et al., U.S. Pat. Nos. 5,971,983, 6,164,283, and 6,245,064 to Lesh, U.S. Pat. No. 6,190,382 to Ormsby et al., U.S. Pat. Nos. 6,251,109 and 6,090,084 to Hassett et al., U.S. Pat. No. 5,938,600 to Swartz et al., U.S. Pat. No. 6,064,902 to Haissaguerre et al., and U.S. Pat. No. 6,117,101 to Diederich et al.
All of the patents and publications cited in this disclosure are incorporated herein by reference.
It is therefore a primary object of some aspects of the present invention to provide improved apparatus and methods for electrically isolating the pulmonary vein by accomplishing a circumferential conduction block surrounding the pulmonary vein ostium in a single ablation application.
It is another object of some aspects of the present invention to reduce the time required to perform electrical isolation of the pulmonary veins.
These and other objects of the present invention are attained by a medical device comprising a catheter introduction apparatus in combination with a radiofrequency emitter that comprises a radially expandable helical coil, which is fabricated from a shape memory alloy. The distal end of the catheter introduction apparatus is placed at a desired location at the ostium of a pulmonary vein. The coil is energized, and an ablation lesion is produced, preferably by the transfer of a single application of radiofrequency energy from the coil to tissue in the ostium of the pulmonary vein.
In one embodiment, the helical coil is expanded by joule heating from a radiofrequency generator to conform to the lumen of the pulmonary vein and to come into a circumferential contacting relationship therewith.
Alternatively or additionally, the helical coil is wrapped about a balloon and is expanded by inflation of the balloon until it is brought into a circumferential contacting relationship with the endothelial surface of the pulmonary vein.
In a further embodiment of the invention, the helical coil is constructed of a biodegradable material, and is left in place following the ablative procedure.
The invention provides a method for electrically isolating a cardiac chamber, including the steps of introducing a coil into a pulmonary vein proximate an ostium of the pulmonary vein, wherein a principal axis of the coil is substantially aligned coaxially with the pulmonary vein, circumferentially engaging the coil with an inner wall of the pulmonary vein to define a circumferential region of contact between the coil and the pulmonary vein, and while maintaining the circumferential region of contact, conducting radiofrequency energy from the coil to the circumferential region of contact to ablate tissue in an ablation region of the pulmonary vein.
In one aspect of the invention, the coil is constructed of a shape memory alloy. When the temperature of the alloy is varied, the coil radially expands to engage the inner wall of the pulmonary vein.
According to another aspect of the method, the when heated, coil becomes tapered, such that the proximal segment of the coil is more radially expanded than the distal segment thereof.
In a further aspect of the method the coil axially expands when heated.
In yet another aspect of the method the shape of the coil is adjusted by differentially heating segments of the coil. Differential heating can be achieved by passing different amounts of current through different ones of the segments of the coil, or by inductive heating.
In still another aspect of the method differential heating is achieved by subjecting the coil to a single electromagnetic influence for heating thereof, and conducting a coolant to selected segments of the coil.
According to still another aspect of the method, a width dimension of the ablation region is at least as large as the pitch of the coil.
An additional aspect of the method introducing includes transferring the coil into the heart through the interatrial septum, and while transferring the coil through the interatrial septum, conducting radiofrequency energy a second time from the coil into the interatrial septum to ablate tissue of the interatrial septum. Radiofrequency energy is conducted the second time until a sufficient amount of the tissue of the interatrial septum has been ablated to accommodate passage of the coil therethrough.
According to yet another aspect of the method, the coil is constructed of a biodegradable material.
In still another aspect of the method radiofrequency energy is conducted to the ablation region in a single continuous application.
In another aspect of the method the coil is circumferentially engaged by disposing the coil about an anchoring balloon, and inflating the anchoring balloon to radially expand the coil. The anchoring balloon can be bilobate or pyriform when expanded.
The method is applicable to hollow viscera other than the heart and the pulmonary veins.